Spark plug



INVENToR gQmC/em msw ` ATTORNEYS.

Aug. 18, 1931. o. MICHELSEN SPARK PLUG Filed Akpril :5. 1929 Patented Aug. 178, 1931 FATE.

WILLIAM OTTO MECHELSE-N, OF WOODHAVEN, NEW YORK SPARK PLUG Application led April 3, 1929. Serial No. 352,185.

This invention relates to new and useful improvements in spark plugs which are especially adapted for use in connection with automobile internal combustion engines.

It is a known fact,-that when starting an internal combustionk engine while it is cold, by means of an electric motor that is supplied with electric current from a battery, which simultaneously is furnishing current for the ignition system of said engine, anarrangement that is generally embodied in the power plant of an automobile, that this battery is often overloaded by the heavy discharge that the starting motor imposes upon it. This heavy discharge is still further increased in cold weather when the oil in the engine is congealed and resists the efforts of the starting motor to a greater extent, eecting a considerable lowering of the voltage Vavailable for ignition of the engine. Frequently the gap formed between the spark plug electrodes, too wide for the purpose of starting the engine, causes failure to produce a spark until after the engine has been turned over a number of times andthe resistance of the crank case oil has thereby'been reduced. This is particularly true when the battery is not fully charged. y

One of the principal objects of my invention is to provide a spark plug which will vary automatically the size of the spark gap in accordance with the temperature of the engine.

' Another object of my invention is to provide the insulator ofthe sparkplug with a recess which surrounds the central electrode in such a manner as to reduce to a minimum the danger of shortcircuiting between the central electrodes, the insulator and the conuctor shell to which the ground electrode is Another object lies in the provision of a stop which cooperates with the movable electrode for limiting the minimum or subnormal size of the spark gap.

A further object liesin the provision of spacedstops for cooperation with the movable electrode to'limit the minimum or subnormal and maximum or normal working sizesof the spark gap.

A still further object lies in the provision of a central electrode and a ground electrode which are -eachformed of a metal Which is expansible under temperature changes and arranged in cooperative relation whereby the same will simultaneously move away from each other and thereby quickly change the spark gap size from a subnormal size to a normal or working size, and to provide spaced stops for each electrode to limit the movements thereof.

With these and other objects in view which will more fully appear, the nature of the infr l ortica vention will be kmore clearly understood by ,s

following t the description, the appended claims, and the several views illustrated in the accompanying drawings.

In the drawings:

Figure l is a longitudinal sectional viewof a spark plug embodying the preferred form of my invention,

Figure 2 is a complete View of the'inner end thereof, Y Figure 3 is a view similar to Figure 1 but showing another form of my invention,

Figure 4: is a complete view of the'inner lend thereof, and

Figure 5 is a complete end view of another form of my invention showing the structures of Figure l and 3 combined.

Like reference numerals designate corresponding parts throughout the severall figures of the drawings.

Referring to the drawings and particularly to Figures l and 2, I have shown a spar plug which comprises a conductor shell A, `an insulator B mounted therein and retained in position by a gland nut C, the inner end 5 of the insulator being disposed within the shell and the outer vend 6 of the insulator projecting for a considerable distancebeyond the gland nut. The outer end 6 of the insulatorv is provided with'an axial opening 7 which communicates with a longitudinally and axially located recess 8, the latter havingan uninterrupted surface and extending from the inner end 5 to a point beyond the gland nut C where it forms a resultant end wall or shoulder 9.

The inner end of the shell A is formed with a reduced and exteriorly threaded extension 10 which constitutes an attaching end for the plug. This extension 10 is provided with an axial recess 11 and mounted in the recess and seated against the wall thereof is a ground electrode comprising a coiled rod or wire 12 of copper or other suitable maerial which will expand and contract under temperature changes, the coil 12 including a plurality of axially alined convolutions. One end 13 of the expansible coil 12 is fixed to the shell A by being mounted within an opening formed therein. The other end oit the coil 12 is bent to form a longitudinally extending shank 14 which terminates in an inwardly and radially extending arm 15.

Axially disposed within the recess 8 oi the insulator B is a central electrode 16 comprising a rod 17 and a terminal arm 18. This rod 17 is substantially co-extensive with the insulator and the shell and the outer end or" to prevent outward movement of the rod relative to theinsulator. The outer end of the rod 17 projects beyond the insulator` and is threaded as at 20. A washer 21 surrounds the threaded outer end of the rod 17 and bears againstthe end of the insulator. If desired an end cap 22 maybe positioned on the rod 17 between the washer 21 and the insulator. Clamping nuts 23 have threaded engagement with the threaded portion 20 of the rod for clamping the flange 19 tightlyV against the shoulder 9. A terminal nut 24 is also engaged with the threaded portion 2O of the rod for cooperation with the clamping nuts 23 to secure ak lead wire 25 to thecentral electrode. If desired, suitable packing may be interposed between the shoulder 9 and the flangev 19. The opposite end of the rod 17 extends through the coiled ground electrode 12 and a transverse opening is formed adjacent the free end of the rod for receiving-the arm 18. This arm 18 extends radially toward the arm 15 and is disposed in overlapping relation thereto to form a resultant spark gap X. The arm 18 is secured in the transverse opening of the rod 17 a driving fitv and consequently this arm may be renewed Whenever desired.

From the foregoing, it. will be observed that when the ground electrode 12 is subjected to heat, the same will expandlongitudinallyy and yconsequently the arm 15 will be moved away from the arm 18 of the central electrodeA and thereby the size of the spark gap will be automatically increased. Normally the arm 15. is located quite close tothe arm 18 so as to form therebetween a spark gap. of subnormal size which will permit the spark to readily pass from one arm to the other when theengine is cold or when rthc battery is not completely charged. In order to limit the minimum or subnormal size of the spark gap, T have provided a stop 26 attached to the extension 10 for cooperation with the shank 14 to limit movement of the arm 15 toward the arm 18. The normal or working size of the spark gap is determined by a stop 27 which is also iixed to the extension 10 for cooperation with the shank 14 to limit movement of the arm 15 away from the arm 18.

The diameter of the recess'S in the insulator is considerably greater than the diameter of the central electrode 16 and consequently an air space is Jformed around that portion of the electrode which is located within the recess. Thus the rod 17 of the central electrode will become completely surrounded by high compressed gases at the time of each spark, and these compressed gases serve as an additional insulation between the rod and the gland nut.

This insulation is especially advantageous should the insulator be formed of porcelainV or other porous material. By reason of the recess 8 extending'beyond the gland nut, l have reduced to ay minimum the possibility of shortcircuiting between the central electrode and the gland nut.

It is to be noted that the minimum distance between the rod 17 and the wall of the recess 8 is greater than the maximum spark gap distance. This is especiallyyaluable in preventing shortcircuiting, as above noted, for the reason that porcelain insulators very soon absorb carbon. The microscopic cracks,

in the glaze become filled with carbon which penetrates the main body of the porcelain and soon causes it to become useless as an insulator.

Referring to Figures 3 and 4 which show another form of my invention, I have dis-- closed a conductor shell A, an insulator Dv arranged therein and held against movementv by a gland nut C. The insulator is formed with a recess 28 similar totherecess 8. The ground electrode29-is iixed tothe shel-l A andl includes an inwardly and radially extending terminal arm 30. Located within the reeess 28 is a central electrode 31 which includes a;

relatively" non-expansible rod 32 and an appreciably expansible rod 33,. the rodsbeing spot welded or otherwise rigidly connected asat 34, 34. The central electrode has its outer end mounted in an axial opening 35 Yformed in the insulator and isheld against longitudinal movements relative to the insulator by an expanded socket 36 formed on the ond oi a projecting rod' 37. The-socket 36 is disposed within a recess 38 formedA in the outerend of the insulator and a packing 39.

nal nut 43 is threaded on the projecting end 37 for cooperation with the nut 42 to clamp a lead wire therebetween.

The free end of the rod 32 of the central electrode extends past the arm 30 of the ground electrode and is spaced therefrom to form a spark gap X. When the rod 33 is expanded longitudinally under the influence of heat, the rod 32 will flex so as to cause the free end thereof to move away from the armk 30 of the ground electrode and thereby automatically increase the size of the spark gap X. In order to limit the minimum and maximum movements of the central elec-- trode, and thereby determine the subnormal and normal widths of the spark gap, I have provided the insulator with spaced stops 44 and 45 respectively.

In the form illustrated in Figure 5, I have combined the structures shown in Figures l and 3 whereby both the central electrode 3l and the ground electrode l2 will be moved simultaneously in opposite directions to quickly increase the size of the gap X whenever heat is applied to the plug.

I claim:

l. In a spark plug, a conducting portion and an insulating portion, two electrodes respectively connected to said portions and forming a spark gap between said electrodes, one of said electrodes including a metal rod having a relatively high coefficient of expansion and movable in a direction under the influence of heat to increase the size ofthe gap, and a stop fixed to one of said members for cooperation with the expansible electrode to limit its movement toward the other velectrode.

2. In a spark plug, a Conducting portion and an insulating portion, two electrodes respectively connected to said portions and forming a spark gap between said electrodes, oneof said electrodes including a metal rod having a relatively high coeflicient of expansion and movable in a direction under theV influence of heat to increase the size of the gap, and spaced stops fixed to one of said members for cooperation with the expansible electrode to limit its extreme movements toward and from the other electrode.

3. In a spark plug, the combination with a conductor shell, of an insulator mounted therein, a central electrode mounted in the insulator, a ground electrode connected to the shell and comprising a coiled rod expansible and contractible under the infiuence of temperature changes, said coil surrounding the central electrode and having one end disposed in cooperative relation to the central electrode to form a spark gap therebetween, and a stop fixed to the shell to limit the movement of the ground electrode in one direction relative to the central electrode.

4. In a spark plug, the combination with a conductor shell, of an insulator mounted therein, a central electrode mounted in the insulator, a ground electrode connected to the shell and comprising a coiled rod expansible and contractible under the influence'of temperature changes, said coil surrounding the central electrode and having one end fixed to theshell and having the other end free and disposed in cooperative relation to the central electrodel to form a spark gap therebetween, anda stop fixedto the shell for cooperation Vwith thefree end of the ground electrode to 4limit the movement thereof toward the central electrode 5. In a spark plug, the combination with a conductor shell, of an insulator mounted therein, and a ground electrode and a central electrode respectively connected to the shell and insulator' and cooperating'to form a spark gap therebetween, said electrodes being formed of metal responsive to heat to thereby effect movements of the electrodes in opposite directions to widen the spark gap. v

6. In a spark plug, the combination with a. conductor shell, of an insulatorL mounted therein, aground electrode and a central electrode respectively connected to the shell and insulator and cooperating to form a spark gap therebetween, said electrodes being formed of metal responsive to heat to thereby effect ymovements of the electrodes in opposite directions to vwiden the spark gap, and stops respectively fixed to the shell and to the insulator and cooperating with the respective electrodes to limit their movements toward each other.

7 Ina spark plug, the combination with a conductor shell, of an insulator mounted therein, a ground electrode and a central electrode respectively connected to the shell and insulator and cooperating to form a spark gap therebetween, said electrodes being formed of metal responsive to heat to thereby effect movements of the electrodes in opposite directions to widen the spark gap, and spaced stops respectively fixed to the shell and to the insulator and cooperating with the respective electrodes to limit their movements toward and from each other.

8. In a spark plug, the combination with a conductor shel1,.of an insulator mounted therein, a central electrode mounted in the in` sulator, and a ground electrode comprising a coiled rod having one end connected to said shell and having its other end disposed in cooperative relation to the central electrode to form a spark gap therebetween, both of said electrodes being formed of metal expansible and contractible under the influence of temperature changes to effect movements of the two electrodes in opposite directions to vary the size of said spark gap.

9. In a spark plug, the combination with therein, a central electrode mounted inthe insulator, and a` ground electrode comprising aeoiled rod disposed within the end of the shell and having one end connected to said shell and having its other end disposed in cooperative relationto the Central electrode tofform a spark gap therebetween, both of said "electrodes being formed of metal eX- pansible and oontrarctible under the influence of temperature Changes to efect movements of the two electrodes in opposite directions to Vary'the size of saidsparl gap.

l0; vIn a spark plug, the oombinationwith a Conductorshell, of an insulator mounted in one end thereof, a central electrode connected at one end to the insulator and having its free end projecting beyond the end of the shell opposite the insulator, a groundk electrode comprising acoiled rod having` a plurality axially alined oonvolutions disposed within the end of the shell opposite the insulator in Contact with the inner wall of said shell and extending around the central electrode, the inner end of the Coil being Connected to the shell and theouterifree end thereof being disposed in cooperative relation to the free end of the central electrode to form a spark gap therebetween,V said coiledv rod being formed of metal responsive to heat to effect movement thereof and thereby vary the size of said spark gap. In testimony whereof,V I have hereunto subscribed my name.

WILLIAM ofrrol Mrornsnsnn.V 

